Wind-induced Stresses Research Articles

Examining Wind Flow's Impact on Multi-Storey Buildings: A Quest for Quality Improvement

Abstract This scientific article delves into the intricacies of wind flow's impact on multi-storey buildings, presenting results from a series of experimental investigations. The research encompasses an examination of wind interactions with buildings of varying heights and geometric profiles. Furthermore, it unveils the effects of tall structures on the natural ventilation and smoke evacuation systems of shorter edifices, considering different wind flow directions. The study leverages specialized wind tunnel and measurement techniques for a comprehensive analysis of wind-induced loads on buildings. The acquired insights furnish crucial input for the design of single-story temporary modular constructions within densely populated urban areas, subject to wind-induced stresses. Additionally, they hold potential applicability in the advancement of energy-efficient technologies and strategies within the realm of construction. The acquired dataset underscores the criticality of scrutinizing wind flow's impact on structures of varied typologies and dimensions and will allow to significantly improve the quality and efficiency of modern buildings in the future.

Study on the Mechanism Effect of Bending Loads on the Decay-like Degradation of Composite Insulator GFRP Core Rod

This paper investigates the deterioration of, and the abnormal temperature rise in, the GFRP core rod material of compact V-string composite insulators subjected to prolonged alternating flexural loading under wind-induced stresses. The axial stress on the GFRP (Glass Fiber Reinforced Plastic) core rod, resulting from transverse wind loads, is a focal point of examination. By establishing a stress model and damage model, the paper simulates and computes the evolution of damage in the outer arc material of composite insulator core rods subjected to alternating flexural loads. Additionally, a multi-factor coupled aging platform is set up, integrating humidity, heat, and mechanical stress, to simulate the crazing deterioration process of composite insulators under alternating flexural loads. Experimental results reveal that during 400,000 alternating load cycles, the core rod underwent stages of surface damage, damage increasing, fatigue embrittlement, matrix hydrolysis, and fiber fracture. Simultaneously, the silicone rubber sheath on the outer side of the composite insulator’s bending arc develops cracks over aging time, creating pathways for moisture ingress into the interface and core rod. The dielectric constant and dielectric loss factor of the aging region of the core rod increase to varying degrees compared to the non-aging part. Moreover, the degree of abnormal heating of the samples intensifies with the duration of aging experiments. These findings underscore the significance of understanding the aging and decay-like fracture process of compact line V-string composite insulators. They provide crucial insights for future research aimed at enhancing the material properties of composite insulator core rods.

Investigating the seismic behavior of multi-story buildings across diverse plan areas and heights using etabs software

The understanding of the behavior of buildings during seismic events is paramount, particularly in regions susceptible to intense earthquakes. Through seismic analysis facilitated by tools like ETABS, engineers can craft structures capable of withstanding seismic forces. ETABS stands out as a versatile solution, accommodating a spectrum of structures ranging from elementary to intricate skyscrapers, whether static or dynamic. Its widespread adoption stems from its ability to cater to diverse building typologies. The engineers leverage ETABS to evaluate the structural integrity of buildings situated in earthquake-prone zones. This entails computing parameters such as sway, displacement patterns, and the magnitude of force the building's foundation must withstand. These analyses are instrumental in guaranteeing the structural resilience of buildings against seismic and wind-induced stresses.

Effect of Distributed Loading and Refined Modeling on Wind-Induced Stress Analysis of Long-Span Bridges

Wind-induced stress analysis is essential for evaluating the local failure and fatigue damage of long-span bridges in wind-prone regions. Nevertheless, the accuracy of stress-level analysis can be affected by the choice of wind loading and structure models. This study formulates three scenarios to calculate the wind-induced response of a long-span bridge, incorporating two types of wind load models (lumped force or distributed force) and two types of finite element (FE) models (spine-beam or substructure). Specifically, Case 1 employs the lumped force and beam model, Case 2 adopts the lumped force and substructure model, and Case 3 utilizes the distributed force and substructure model. The aerodynamic parameters for forces and POD pressure modes are obtained through wind tunnel tests. By comparing the wind-induced structural response in terms of global behavior (displacement, acceleration) and local behavior (stress), the influence of wind loading and structure models is discussed. The findings reveal that employing a simplified beam model underestimates local stress, and neglecting wind load distribution leads to further underestimation. Therefore, the refined FE model and distributed wind load models are recommended for the precise assessment of wind-induced stresses in long-span bridges.

Aerodynamics and aeroelastic performance of a rigid-frame bridge with a bluff body girder subjected to short-rise-time gusts

Short-rise-time gusts in mountainous areas are extreme winds with the characteristics of rapidly varying wind speeds and directions, strong suddenness, and large angles of attack. Currently, studies on long-span bridges under short-rise-time gusts in mountainous areas, especially experimental studies, are limited. In this study, a typical long-span rigid-frame bridge with a bluff body girder located in a mountainous area suffering from frequent gusts was selected. Corresponding sectional and full aeroelastic model tests in a multiple-fan active control wind tunnel were performed to investigate the aerodynamic forces and wind-induced responses under strong gusts. Two aerodynamic measures (i.e., flange slab and stabilizing plate) were applied to mitigate the impact of gusts on the studied bridge. Moreover, numerical simulation analysis was also carried out to investigate the effects of gusts on the wind-induced stresses. The experimental results demonstrated that the gust parameters significantly affect the aerodynamic forces and wind-induced responses of the long-span rigid-frame bridge, especially under construction, although this type of bridge usually shows less wind-related sensitivity under normal monsoon climates. Furthermore, the proposed aerodynamic measures effectively mitigated the displacement responses of the studied bridge subjected to gusts in mountainous areas. This investigation can provide a more comprehensive understanding of the aerodynamics and aeroelastic performance of similar bridges under gusty conditions.

Fluid-structure interaction of a tensile fabric structure subjected to different wind speeds

Despite the current technologic developments, failures in existent tensile fabric structures (TFS) subjected to wind do happen. However, design pressure coefficients are only obtained for large projects. Moreover, studies on TFSs with realistic supporting frames, comparing static and dynamic analyses and discussing the design implications, are lacking. In this study, fluid-Structure analyses of a TFS supported by masts and inclined cables, by subjecting it to different wind speeds, are carried out, to gain more understanding in the above-referred aspects. Wind-induced stresses in the fabric and axial forces in masts and cables are assessed for a hypar by using computational fluid dynamics. Comparisons are carried out versus an equivalent static analysis and also versus loadings deemed representative for design. The procedure includes the so-called form-finding, a finite element formulation for the TFS and the fluid formulation. The selected structure is deemed realistic, since the supporting frame is included and the shape and geometry of the TFS are not uncommon. It is found that by carrying out an equivalent static analysis with the determined pressure coefficients, differences of up to 24% for stresses in the fabric, 5.4% for the compressive force in the masts and 21% for the tensile force in the cables are found with respect to results of the dynamic analysis. If wind loads commonly considered for design are used, significant differences are also found, specially for the reactions at the supporting frame. The results in this study can be used as an aid by designers and researchers.

Fracture and mixed-mode resistance curve behavior of bamboo

Bamboo is a natural composite abundantly available in the world, and is a source of inspiration for design of new construction materials and structural composites for many applications. The microstructure of this Functionally Graded Material (FGM) evolves through its thickness in response to wind-induced stresses that arise in the plant during its lifetime. This paper presents the results of an experimental study on the structure and toughening mechanisms in Moso culm bamboo. The hierarchical and multi-scale structure of bamboo and the distribution of micron scale fibers are revealed via optical microscopy. Four-point bend fracture experiments are performed where the applied crack-driving forces are computed as a function of crack length. This experimental data are incorporated within a finite element framework in order to understand the fracture and deformation mechanisms of bamboo, and compute the Resistance-curves (R-curve)s. The resistance-curve behavior is shown to be dependent on the orientation of the fibers. In cases where the fibers are perpendicular to the crack growth toughening is observed to occur via crack bridging. Intermediate shielding levels are observed when toughening occurs by crack deflection for crack growth along the fiber orientation.

Improving statistical windthrow modeling of 2 Fagus sylvatica stand structures through mechanical analysis

In 1999, the major windstorm, Lothar, damaged many beech stands on the French Lorraine limestone plateau. Some of them were coppices with standards (CWS) while others were high forest (HF) stands. The use of statistical models to compare the wind firmness of different stand structures is often limited by poor estimates of the individual wind loading. Available knowledge about the mechanics of windthrow processes such as wind loading could improve statistical modeling. Our aim was to identify the main trees and site risk factors for beech and to compare wind firmness of both stand structures by fitting such a model. We developed a windthrow model with mixed effects, which is based on a simplified mechanical analysis of the wind-induced stresses and Weibull’s theory of fracture. This analysis revealed the relevancy of including the product of the crown diameter and the square of the tree height, known as the bending moment coefficient, in the model. The Weibull-based model was compared with multiple logistic regressions. Both models were fitted using tree and site factors on 384 dominant beeches (196 in CWS and 188 in HF) from 51 plots with comparable site conditions between the two stand structures.Damage mainly increased with tree height, although it also slightly increased with crown width. The bending moment coefficient used in the Weibull-based model more effectively accounted for tree size and tree shape effects than the logistic regressions.Stand structure showed an interesting second-order effect since the increase of risk with the increase of the bending moment coefficient was higher for HF. Including a random plot effect significantly improved the model likelihood and, therefore, took partly wind-induced spatial variability into account. To apply Weibull’s theory to windthrow, many assumptions that require further investigation must be made regarding the brittle behavior and the distribution of stresses in the root-soil plate.

On-line monitoring of wind-induced stresses and fatigue damage in instrumented structures

SUMMARY The use of sparse-measured response as a means to monitor stresses and fatigue damage throughout metal structures has been the subject of recent work by researchers in the !eld of vibration-based structural health monitoring. The basic premise is that by using measured structural response, one can improve upon purely stochastic estimates. The most recent applications found in the literature employ the Kalman !lter as an estimator. In this paper, we propose a !nite element model-based state estimator that can be implemented as a modi !ed version of the !nite element model of the system using corrective forces that are proportional to the measurements. In contrast with the standard Kalman !lter, the proposed estimator explicitly accounts for spatial correlation and for the colored nature of the excitation through knowledge of its power spectral density. The approach is used to estimate the number of threshold crossings in the bending moment history of a simulated tall vertical structure subject to turbulent wind. It is shown that the proposed model-based estimator outperforms a standard Kalman !lter. Copyright © 2012 John Wiley & Sons, Ltd. Received 28 February 2012; Revised 7 September 2012; Accepted 17 October 2012

Leonardo’s Rule, Self-Similarity, and Wind-Induced Stresses in Trees

Examining botanical trees, Leonardo da Vinci noted that the total cross section of branches is conserved across branching nodes. In this Letter, it is proposed that this rule is a consequence of the tree skeleton having a self-similar structure and the branch diameters being adjusted to resist wind-induced loads.

Developing a Simple Damage Model for the Long-Term Durability of Acrylic Foam Structural Glazing Tape Subject to Sustained Wind Loading

AbstractThis article presents a simple linear damage accumulation model that may have applicability for predicting damage from sustained winds in double-sided acrylic foam tape used to attach curtain wall glazing panels to buildings. The purpose of this model is to investigate the possible cumulative effects of years of wind-induced stresses that are less than the peak stress expected during a 3-s gust, as specified in current design guidelines established by the structural glazing industry and adopted by the manufacturer of these structural glazing tapes. Several representative wind histories are selected to provide input data for the model. These wind histories provide multiple years of average wind speeds over either 10-min or 1-h recording intervals, depending on the source. Each entry in a wind speed history is converted to stress on the glazing adhesive tape on assumed window dimensions using the standard wind loading design equations of ASCE 7-05. A creep rupture prediction equation, developed from...

Experimental Determination of Wind-Induced Response on a Model of Natural Draught Cooling Tower

The detailed and well-publicized documented paper by Bamu and Zingoni in 2005 on cooling-tower collapses accentuates the effect of wind on the performance of cooling towers. As it is well established that wind-tunnel tests on tower models result in a more realistic assessment of wind-induced stresses, wind-tunnel tests are conducted on aero-elastic model of an isolated cooling tower and the cooling tower with surrounding structures. The details of the experimental programme, measurements, analysis, and results for both the isolated and interference cases are presented in this paper. Based on the analysis of experimental data, ring-resonance frequencies, and mode shapes of the model, meridional (Nϕ) and hoop (Nθ) stress resultants and interference factor due to the presence of surrounding buildings are evaluated. The values of Nϕ, Nθ, ring-resonance frequencies, and mode shapes for isolated model are further compared with the values obtained based on finite element analysis.

On the validity of thermal wind balance in alongshelf currents off the New Jersey coast

The validity of thermal wind balance (TWB) as an approximation for the observed vertical shear in coastal currents (depth 10–30 m) is analyzed based on the ADCP and CTD transects conducted off the New Jersey coast in early August of 1996. At that time, the study area was forced simultaneously by a brief upwelling-favorable wind event and the arrival of a buoyant plume from the Hudson Estuary. As a result, both downwelling- and upwelling-favorable alongshelf currents resided within the same area, the former inshore and the latter offshore. The very intense pycnocline (buoyancy frequency ∼0.06 s −1) was shaped as a dome and thus the TWB shear of both signs was observed within the same across-shelf transects and under the same wind conditions. In average, the geostrophic (TWB) shear overestimated the observed by a factor of 2. The maximum of the ageostrophic shear (which is the observed minus TWB shear) was within the sloping pycnocline and not near the bottom (where one would expect to find a strong frictional shear). For both upwelling and downwelling-favorable currents, the geostrophic shear had a sharp maximum in the pycnocline (localized within a few meters), while the ageostrophic shear tended to smooth the actual velocity profile, counteracting the TWB shear in the pycnocline and adding to it (changing sign) below. The result was a more linear velocity distribution with depth compared to the TWB prediction. The significant reduction of the TWB shear in the pycnocline described in this study was likely related to the turbulence production by the internal wave breaking. The wind-induced stresses were trapped in the shallow, ∼5 m deep surface layer, and were inhibited below by a strong pycnocline. Nonfrictional mechanisms (inertia or momentum advection) did not contribute significantly to the ageostrophic shear.

The Effects of Wind Forcing and Pycnocline Stresses on Zonal Currents in the Western Equatorial Pacific

Abstract Simultaneous moored temperature, salinity, velocity, and wind measurements from the equator at 157.5°E, during 10 May–21 December 1992, are combined with a no-stress-level boundary condition in the Equatorial Undercurrent core to estimate the total zonal pressure gradient force and subgrid-scale residuals of the momentum balance. Estimates are made of the depth of wind stress penetration, momentum depth, distribution of subgrid-scale stresses, and balance of forcing terms in the surface layer and pycnocline. Westerly winds of greater than 5 m s−1 in September 1992 coincided with the appearance of an eastward surface Yoshida jet and subsurface westward (Hisard) jet on the equator. The momentum depth increased with successive wind events, eroding the shallow halocline until it merged with the permanent thermocline. Wind-induced stresses were not restricted to the depth of density homogenization. The record-length-averaged pressure gradient force was westward and was balanced by downstream accelerat...

Wind-induced interference effects on two adjacent cooling towers

This paper presents the results of experimental tests carried out in the boundary layer wind tunnel (BLWT) on a rigid model of two adjacent cooling towers. Pressures measured on the two towers were compared with those registered on an isolated tower. The variation of the flow-induced forces produced on each tower by the other one is referred to as interference. Using the registered pressures, numerical linear analyses were performed to calculate the structural responses of the isolated and grouped towers. The results obtained agree with those of other researchers and demonstrate the reliability of the procedure adopted to estimate wind-induced stresses on rigid structures in close proximity.

Comments on “Wind-induced stresses in cherry trees: evidence against the hypothesis of constant stress levels” by K.J. Niklas, H.-C. Spatz, Trees (2000) 14:230–237

Comments on “Wind-induced stresses in cherry trees: evidence against the hypothesis of constant stress levels” by K.J. Niklas, H.-C. Spatz, Trees (2000) 14:230–237

Wind-induced stresses in cherry trees: evidence against the hypothesis of constant stress levels

We calculated the wind-induced bending moments and stresses generated in the stems of five Prunus serotina conspecifics differing in height and canopy shape and size (based on detailed measurements of stem projected area and location with respect to ground level) to test the hypothesis that wind-loads generate uniform and constant stress levels along the lengths of tree twigs, branches, and trunks. These calculations were performed using five different wind speed profiles to evaluate the relative importance of the shape of wind speed profiles versus the ’geometry’ of tree shape on stem stress distributions and magnitudes. Additionally, we evaluated the effect of absolute tree size and stem taper on wind- induced stresses by scaling the size of smaller conspecifics to the absolute height of the largest of the five trees yet retaining the original stem proportions (i.e., diameter relative to stem length) for each plant. Finally, we also determined how the factor of safety for wind-loading (i.e., the quotient of stem yield stress and wind-load stress) changed as a function of tree size (and, presumably, age). Our results indicate that wind-load stress levels (1) vary along stem length even for the same wind speed profile and the same maximum wind speed; (2) would increase to dangerous levels with increasing tree height if it were not for ontogenetic changes in stem taper and canopy shape that reduce stress intensities to manageable levels; (3) tend to be more dependent on stem taper and canopy shape and size than on the shape of the wind speed profile; and (4) the factor of safety against wind-induced mechanical failure decreases as trees get larger, but varies along the length of large trees such that preferential stem failure is likely and functionally adaptive. We thus (1) reject the hypothesis of constant wind-induced stress levels; (2) support the view that size-dependent changes in stem taper are required to maintain wind-load mechanical reliability; and (3) suggest that certain portions of mature trees are ’designed’ to fail under high winds speeds, thereby reducing drag and the bending moments and stresses experienced by trunks.

A three dimensional-circulation model of Lake Tanganyika

A combination of field measurements and computer modelling was selected as a main approach, when the Hydrological Subcomponent of the Lake Tanganyika Research (LTR) Program was established. The main goal of the modelling work is to estimate the role of main factors affecting water currents in Lake Tanganyika and to understand the peculiarities of spatial and temporal variations of its hydrophysical characteristics. Special attention is given to a more accurate description of wind-induced shear stresses, the main driving force of the lake dynamics. Numerical experiments with a mesoscale meteorological model show the significant role of a coastal diurnal slope-lake breeze system, intensified during the dry season while south-easterly trade winds supply the main amount of energy to the middle of the lake.

Tide and surge dynamics along the Iberian Atlantic coast

The eastern Atlantic barotropic dynamics (in a region spanning from 20° N to 48° N and 34° W to 0°) are studied through numerical modelling and in situ measurements. The main source of data is the tidal gauge network REDMAR, managed by Clima Marítimo (Puertos del Estado). The numerical model employed is the HAMSOM, developed both by the Institut für Meereskunde (Hamburg University) and Clima Marítimo. In this paper, tidal and storm surge dynamics are studied for the region, focusing particularly on the nonlinear transfer of energy between the different forcings. The results of tidal simulations show good agreement between semidiurnal harmonic components and the values obtained from the tidal gauges (both coastal and pelagic) and current metres. The nonlinear transfers of energy from semidiurnal to higher order harmonics, such as M4 and M6, were mapped. Those transfers were found to be important in only two areas: The French continental shelf in the Bay of Biscay and the widest part of the African shelf, south of Cabo Bojador. The modelled diurnal constituents show larger relative differences with measurements than semidiurnal harmonics, especially in data concerning the phase. A method to isolate the nonlinear transfers of energy between tidal and atmospheric forcing during a storm surge was developed. These transfers were found to be significant in the same areas where tidal nonlinear activity was present. The effect of short period wind generated waves on sea surface elevation was also investigated. The magnitude of the spatial derivatives of radiation stress was compared with wind-induced stress. As a result of this comparison, we found the inclusion of a forcing term that depends on radiation stress in ocean model simulations at this scale and resolution to be not essential. The effect of computing wind-induced stresses, with a formulation that explicitly depends on sea state, was also explored by means of a coupled run of the HAMSOM and the spectral wave model WAM for a storm surge event in the Spanish coast. This formulation was not found to be an improvement over a classical parameterisation which only depends on wind fields.

Site Relationships for Some Wood Properties of Pine Species in Plantation Forests of Southern Africa

SYNOPSIS Although genetic variation in wood properties of the three main pine species planted in southern Africa is high, there are important site relationships. Density. A study of density in Pinus patula on 147 sites in the main forestry region showed that wood formed during the early years was influenced mostly by soil properties, whereas wood formed later in the rotation was influenced more by climate. Density gradient was more closely related to site than was inner density, outer density or mean density. Spirality. The same study indicated that spirality decreased as site quality improved. Stem bumps. Nodal swellings in P. patula increase in size with age, affecting strength properties and veneers. Regression models contained site variables strongly related to stem stability and to exposure. It was concluded that bumps are a reaction by the tree to wind-induced stresses at the zones of greatest weakness, viz. at the nodes. Heart shake. Resin-infiltrated heart shakes cause severe losses in the recover...